The present invention relates generally to the manufacture of recording elements used to retrieve information from disks, tapes and other magnetic media. In particular, the present invention relates to the construction of read heads. More particularly, the present invention relates to a method of making magnetic read heads that use magnetoresistive material.
It is known in the art to use magnetoresistive material as part of a magnetic read head. Typically, a thin rectangular sheet of magnetoresistive material referred to as a stripe is used to sense the magnetic field stored on the recording medium. The magnetoresistive (MR) stripe is preferably mounted in a plane perpendicular to the recording medium. The MR stripe has a conductor lead attached at each opposite end. The conductor leads carry a constant sense current through the MR stripe. The current enters through one lead, continues along the stripe, and exits from the second lead. The MR stripe senses the magnetic field presented by the recording medium because the resistivity of the MR stripe changes depending on the direction of magnetization of the field. Therefore, if the current applied remains constant, changes in the voltage across the MR stripe will reflect changes in the magnetic field applied by the recording medium since the changes in voltage correspond to changes in the resistance of the MR stripe.
In a dual stripe magnetic read head, two magnetoresistive stripes measure the field presented by magnetic medium. Preferably, both stripes are placed perpendicular to the magnetic recording medium and parallel to each other. For proper operation of the dual stripe magnetic head and for biasing purposes, the two MR stripes must be precisely aligned and placed as close together as possible, yet electrically insulated.
Methods known in the art usually construct dual stripe magnetic heads by fabricating the stripes one on top of another with an insulator between on the same wafer. Fabrication methods such as vacuum deposition and photolithography are often used to construct dual stripe MR heads because each stripe is very thin, typically on the order of 200 angstroms, and must be positioned very accurately.
The prior art methods of constructing of a dual stripe magnetoresistive head typically begin with a wafer that has a planar surface. If the wafer is magnetic ferrite, which would act as the MR shield, the first layer deposited on the wafer would be the bottom gap, usually aluminum oxide. If a non-magnetic substrate is used, then a soft magnetic material would be the first layer, which would establish a shield for the MR layer, and then the bottom gap is deposited on top of it. A layer of magnetoresistive material is deposited on the wafer to form a first MR stripe. Next, a layer of conductive material is deposited on the surface of the wafer to form two conductor leads. The leads are positioned so that the first MR stripe is deposited so that it electrically connects the two conductor leads. The surface of the wafer, the conductor leads, and the first stripe are then covered with a layer of insulation. Another layer of magnetoresistive material is deposited on the insulation to form a second stripe. Layering techniques like vacuum deposition and photolithography are used to construct the head because they allow the second stripe to be positioned parallel to and directly above the first stripe. Another layer of conductor material is then deposited on the insulation to form two conductor leads with the second stripe interconnecting the leads. A top gap is deposited on top of the second stripe, preferably the same thickness and material as the bottom gap. Next, the parts are cut out and a superstrate of ferrite is placed on top. If the superstrate is non-magnetic, then a soft shield is deposited on the top gap and then the superstrate is placed on top. In tape heads, non-conducting nickel zinc ferrite is typically used as the substrate and supersubstrate to eliminate the chance of shorting.
As the need to place the magnetoresistive stripes closer together for proper biasing and for increased sensitivity of heads has developed, several problems have arisen with the methods currently known for constructing dual stripe magnetic heads. The methods presently used to construct dual stripe magnetic heads often fail to keep the stripes and leads electrically insulated when the stripes are placed very close together. With the prior art method described above, there is a high probability that the stripes will short-circuit because the insulation between them is very thin. When the second stripe and its leads are deposited on top of the insulation and first stripe, it often penetrates through the insulation making contact with the other stripe and its leads.
Another problem with prior art construction methods is that the thickness and composition of the two stripes often varies. For optimum performance of the head, the two stripes should have the identical thickness and composition. However, the prior art deposits the stripes in two separate layering processes. For example, after the first stripe has been deposited in a layering process, a layer of insulation is placed over the stripe, and then the second stripe is deposited in another layering process. This results in inconsistencies in thickness and composition of the stripes because it is difficult to achieve the same thickness and composition for the stripes when they are deposited in different layering processes.